When native bulk substrates are not available or are too expensive, materials useful for semiconductor devices are often formed by heteroepitaxy on seed substrates. The seed substrates often have unsuitable atomic lattice spacing and coefficients of thermal expansion with respect to the material to be grown that can result in detrimental effects on material quality. For example, layers grown on seed substrates can have high dislocation densities, cracks, and compression or tensile strains, all of which lead to reduced efficiency of devices subsequently manufactured on them.
Thus, in the art, compliant layers, e.g., low-viscosity layers, have been provided between hetero-epitaxial films and final substrates so that strains can be released by subsequent heat treatment. See, e.g., Hobart, K. D. et al., “Compliant Substrates: A Comparative Study of the Relaxation Mechanisms of Strained Films Bonded to High and Low Viscosity Oxides”, Journal of Electronic Materials, Volume 29, No. 7, 2000, pages 897-900.
However, presently used methods for the relaxation of strained hetero-epitaxially-grown films often not show satisfying results with respect to the suppression of buckling, etc. Moreover, the transfer of heteroepitaxial films grown on a seed substrate (or growth substrate) to a final substrate for the manufacture of semiconductor devices is beset by problems, including the problems of maintaining the heteroepitaxial films intact, and of removing the seed substrate without damaging the heteroepitaxial films.
Therefore, improved methods for the formation of reliably relaxed and intact strained films, or islands of such films, on target substrates that have the quality required for the fabrication of semiconductor devices would be advantageous.